Fix edge case in stack trace formatting.

Fix edge case in stack trace formatting.

Bug description: in strict mode, null as receiver is not implicitly converted
to the global object, so that when formatting the stack trace, the receiver of
the stack frame is null. The IS_OBJECT check returns true for null, but
%GetDataProperty expected a JSObject, which results in a failed RUNTIME_ASSERT.

R=mvstanton@chromium.org
BUG=237617
Committed: https://code.google.com/p/v8/source/detail?r=14797

[mvstanton, 2013-05-24 10:57:27]

Looks good, lgtm.

[Yang, 2013-05-24 11:33:53]

Committed patchset #1 manually as r14797 (presubmit successful).